1. Field of the Invention
The present invention relates to an optical disk drive which drives a recordable optical disk, and more particularly to a CD encode device for such an optical disk drive.
2. Description of the Related Art
An optical disk is widely used as a device capable of storing a huge amount of information.
First, a description will be given of an outline of an optical disk and a drive structure.
General CD-R and CD-E disks are writable (recordable) CDs (Compact Disks). The CD-R (CD Recordable) is a CD on which information can be recorded only once (also called CD-Write Once). The CD-E (CD Erasable) is a CD on which information can repeatedly be recorded a plurality of numbers of times (also called CD-RW: CD ReWritable). Information can be recorded on and reproduced from the CD-R and CD-E, namely, optical disks by means of a drive as shown in FIG. 1.
FIG. 1 is a function block diagram of an optical disk drive. The optical disk drive is made up of an optical disk 1, a spindle motor 2, an optical pickup, a motor driver 4, a read amplifier 5, a servo unit 6, a CD decoder 7, an ATIP (Absolute Time In Pre-groove) decoder 8, a laser controller 9, a CD encoder 10, a CD-ROM encoder 11, a buffer RAM 12, a buffer manager 13, a CD-ROM decoder 14, an ATAPI/SCSI interface 15, a D/A converter 16, a ROM 17, a CPU 18 and RAM 19. In FIG. 1, a symbol LB indicates a laser beam, and Audio denotes an audio output signal.
The arrows shown in FIG. 1 generally indicate the directions of flows of data. For the sake of simplicity, FIG. 1 is illustrated so that a thick solid line extends from the CPU 18 for controlling the blocks and thus individual lines provided between the CPU 18 and the blocks are omitted.
The structure and operation of the optical disk drive are as follows.
The optical disk 1 is driven to be rotated by the spindle motor 2, which is regulated at a constant linear velocity by the motor driver 4 and the servo unit 5. The linear velocity can be changed stepwisely. The optical pickup 3 includes a semiconductor laser diode, an optical system, a focus actuator, a track actuator, a light-receiving element and a position sensor, these built-in components being not depicted. The optical pickup 3 projects the laser beam LB onto the optical disk 1. The optical pickup 3 can be transported in the sledge direction by a seek motor. The focus actuator, the track actuator and the seek motor are controlled so that, based on the signals from the light-receiving element and the position sensor, the spot of the laser beam LB is located on the target position by the motor driver 4 and the servo unit 5.
At the time of a read operation, a reproduced signal obtained by the optical pickup 3 is amplified by the read amplifier 5 and is binarized. The resultant binarized reproduced signal is input to the CD decoder 7. The input binarized data is subjected to an EFM (Eight to Fourteen Modulation) process by the CD decoder 7. The data recorded on the optical disk 1 is obtained by an EFM modulation which is carried out every eight bits. In the EFM modulation, eight-bit data is converted into fourteen-bit data, to which three associated bits are added, so that the total number of bits are 17. The associated bits are given so that the number of bits "1" and the number of bits "0" appearing up to now is equal to each other in average. This is called "suppression of DC component", and a variation in the slice level of the reproduced signal from which the DC component is cut off can be suppressed.
The demodulated data is then subjected to deinterleave and error correction processes.
Then, the resultant data is input to the CD-ROM decoder 14 and is further subjected to an error correction in order to enhance the reliability of the demodulated data.
The data obtained by the two error correction processes is temporarily stored in the buffer RAM 12 by the buffer manager 13. When the amount of data sufficient to form sector data is available in the buffer RAM 12, the data is transferred to a host computer (not shown) via the ATAPI/SCSI interface 15 without interruption.
If the data is music data, the data output from the CD decoder 7 is input to the D/A converter 16, and is output as analog audio signal.
At the time of a write operation, data supplied from the host computer through the ATAPI/SCSI interface 15 is temporarily stored in the buffer RAM 12 by the buffer manager 13. When a certain amount of data becomes available in the buffer RAM 12, the write operation is started. In this case, it is required to move the laser spot to a write starting position. This write starting position can be obtained from a Wobble signal that is stamped beforehand on the optical disk 1 by snaking of tracks.
The Wobble signal includes absolute time information called ATIP, which is extracted by the ATIP decoder 8. A synchronizing signal generated by the ATIP decoder 8 is input to the CD encoder 10, whereby the writing of data can be carried out at the correct position on the optical disk 1.
The data stored in the buffer RAM 12 is subjected to an error correction adding process and an interleave process by the CD-ROM encoder 11 and the CD encoder 10, and is then recorded on the optical disk 1 through the laser controller 9 and the optical pickup 3.
The EFM modulated data drives, as a bit stream, the laser diode at a channel bit rate of 4.3218 Mbps (standard bit rate). In this case, the recorded data forms an EFM frame every 588 channel bits. A channel clock is defined as a clock of the frequency equal to that of the channel bits.
The above is the outline of the structure and operation of the optical disk drive shown in FIG. 1.
A one-chip LSI device used for an optical disk, for example, used in the CD-F drive has been marketed (for example, LC8959 manufactured by SANYO DENKI KABUSIKI KAISHA). The one-chip LSI device includes a CD decode system circuit (which processes a signal read from the disk) and a CD encode system circuit (which processes a signal based on write data to be actually written onto the disk). The CD decode system circuit and the CD encode system circuit operate in synchronism with respective different clock signals. That is, the one-chip LSI device requires two different clock signals.
Generally, two oscillation elements are required to generate the two different clock signals. Since oscillation elements are not less expensive, the use of the above one-chip LSI device increases the production cost.